A6210 Datasheet

A6210
3 A, 2 MHz Buck-Regulating LED Driver
Features and Benefits
Description
▪ User-configurable on-time, achieving switching
frequencies up to 2.0 MHz
▪ Brightness control through PWM of DIS pin
▪ Minimal external components required
▪ No output capacitor required
▪ Wide input voltage range: 9 to 46 V
▪ Low 0.18 V sense voltage for higher efficiency
▪ Output Current: up to 3.0 A
▪ Low standby current <100 μA
▪ Thermal shutdown
▪ Supplied in a thermally-enhanced 4 mm QFN package
The A6210 is a buck regulator that uses valley current-mode
control. This control scheme allows very short switch on-times
to be achieved, making it ideal for applications that require
high switching frequencies combined with high input voltages
and low output LED span voltages.
Low system cost is accomplished through high switching
frequencies of up to 2.0 MHz, allowing smaller and lower value
inductors and capacitors. In addition, few external components
are required through high levels of integration. Optimal drive
circuits minimize switching losses.
The switching frequency is maintained constant, as the on-time
is modulated by the input voltage. This feed-forward control
ensures excellent line correction. The on-time is set by an
external resistor pulled-up to the input supply.
Applications:
▪ High brightness LEDs
▪ LED driver modules, power supplies and lamps, such as
MR16 and MR11
Internal housekeeping and bootstrap supplies are provided
which require the addition of only one small ceramic capacitor. A
top-off charge pump ensures correct operation at light loads.
Package 16-contact QFN (suffix EU):
Internal diagnostics provide comprehensive protection against
input undervoltages and overtemperatures.
The device package is a 16-contact, 4 mm × 4 mm, 0.75 mm
nominal overall height QFN, with exposed pad for enhanced
thermal dissipation. It is lead (Pb) free, with 100% matte tin
leadframe plating.
4 mm × 4 mm × 0.75 mm
Typical Application
VIN
24 V
R1
150 kΩ
BOOT
VIN
C1
1.0 μF
C2
22 nF
L1
68 μH
LX
TON
D1
A 6210
ISEN
LED2
R2
390 mΩ
PWM or Switch
DIS
6210-DS, Rev. 2
LED3
SGND
NC
LED span voltage = 10.5 V
Average LED current = 500 mA
Peak to peak current = 60 mA
Switching frequency = 1.4 MHz
Efficiency = 90.5%
LED1
GND
Suggested Parts
Name
C1
C2
D1
L1
R1
R2
Description
Manufacturer - Part Number
1 μF, 25V, X5R or X7R ceramic, 1210
22 nF, 50V, X5R or X7R ceramic, 0805
1 A, 30 V, Schottky diode
68 μH, 1 A inductor
180 kΩ, 1%, 0805
390 mΩ, 1%, 0805
Taiyo Yuden, TDK
Taiyo Yuden - NR 6045T 680M
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Selection Guide
Part Number
A6210GEUTR-T
Packing
1500 pieces per reel
Package
16-contact 4 mm × 4 mm QFN with exposed thermal pad
Absolute Maximum Ratings (reference to GND)
Characteristic
VIN Pin Supply Voltage
LX Pin Switching Node Voltage
ISEN Pin Current Sense Voltage
Symbol
Notes
Rating
Units
–0.3 to 50
V
VLX
–1 to 50
V
VISEN
–1.0 to 0.5
V
VIN
DIS Pin Disable Voltage
VDIS
–0.3 to 7
V
TON Pin On-Time Voltage
VTON
–0.3 to 50
V
Operating Ambient Temperature
TA
–40 to 105
ºC
Maximum Junction Temperature
TJ(max)
150
ºC
Tstg
–55 to 150
ºC
Storage Temperature
Range G
Recommended Operating Conditions
Min.
Typ.
Max.
Supply Voltage
Characteristic
Symbol
VIN
Conditions
9
–
46
Units
V
Switching Node
VLX
–0.7
–
46
V
Switching Frequency Range
fSW
0.1
–
2.0
MHz
Operating Ambient Temperature
TA
–40
–
105
ºC
Junction Temperature
TJ
–40
–
125
ºC
Continuous conduction mode
Thermal Characteristics may require derating at maximum conditions, see application information
Characteristic
Symbol
Package Thermal Resistance,
Junction to Ambient
RθJA
Package Thermal Resistance,
Junction to Pad
RθJP
Test Conditions*
Value
Units
On 4-layer PCB based on JEDEC standard
36
ºC/W
On 4-layer PCB based on JEDEC standard
2
ºC/W
*Additional thermal information available on the Allegro website.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Functional Block Diagram
VIN 24 V
C2
22 nF
C1
1.0 μF
BOOT
VIN
Top-off
Charge
Pump
Linear
Regulator
VIN
Sleep
Circuit
R1
180 kΩ
L1
68 μH
LX
LED1
Driver
D1
TON
On
Timer
Control
Logic
Off
Timer
LED3
ISEN
Blank
DIS
R2
390 mΩ
Regulator
Comparator
Switch
Closed = On
LED2
SGND
VIN UVLO
Linear OK
+
Fault
TSD
Reg
Ref
–
GND
NC
Switching Frequency = 1.4 MHz
All capacitors are X5R or X7R ceramic
Resistor R2 should be surface mount, low inductance type, rated at 250 mW at 70°C
Terminal List Table
VIN
1
13 NC
14 NC
15 NC
16 NC
Pin-out Diagram
12 LX
NC
2
TON
3
10 DIS
GND
4
9
11 BOOT
8
ISEN
7
NC
6
GND
GND
5
PAD
(Top View)
Number
Name
1
VIN
Input supply
Function
2, 7, 13, 14,
15, 16
NC
No connection; tie to GND
3
TON
Terminal for on-time setting with external resistor
4, 5, 6
GND
Ground terminal
8
ISEN
Current sense input
9
SGND
Current sense ground reference
SGND
10
DIS
11
BOOT
12
LX
–
PAD
Disable/enable logic input; active high
Bootstrap supply node
Switch node
Exposed thermal pad; connect to ground plane
(GND) by through-hole vias
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A6210
3 A, 2 MHz Buck-Regulating LED Driver
ELECTRICAL CHARACTERISTICS* valid at TJ = 25°C, VIN = 9 to 46 V, unless otherwise noted
Characteristic
Symbol
Conditions
Min.
Typ.
Max.
Units
–
–
100
μA
General
VIN Quiescent Current
IVINOFF
Current Sense Voltage
VSENSE
On-Time Tolerance
∆TON
DIS = high, VIN = 46 V
Based on selected value
176
183
190
mV
–15
–
15
%
Minimum On-Time Period
Ton(min)
–
50
60
ns
Minimum Off-Time Period
Toff(min)
–
–
350
ns
Start-Up Time
tSTART
Using application circuit on page 1; time from
application of D̄¯¯¯IS̄¯ (enable) to reaching target current
–
15
–
μs
Buck Switch On-Resistance
RDS(on)
TJ = 25°C, ILOAD = 3 A
–
350
–
mΩ
TJ = 125°C, ILOAD = 3 A
–
550
–
mΩ
VDIS
Device enabled
–
–
1
V
VDISOC
Device disabled
2
–
7
V
DIS = 0 V
–10
–
–1
μA
Voltage rising
6.3
–
7.5
V
0.7
–
1.1
V
Temperature rising
–
165
–
°C
Recovery = TJTSD – TJTSD(hys)
–
15
–
°C
Input
DIS Input Voltage Threshold
DIS Open-Circuit Voltage
DIS Input Current
IIN
Protection
VIN Undervoltage Shutdown Threshold
VINUV
VIN Undervoltage Shutdown Hysteresis
VINUV(hys)
Overtemperature Shutdown Threshold
TJTSD
Overtemperature Shutdown Hysteresis
TJTSD(hys)
*Specifications
over the junction temperature range of –40°C to 125°C are assured by design and characterization.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Functional Description
Basic Operation
The A6210 is a buck regulator that utilizes valley current mode
control. The on-time is set by the amount of current that flows
into the TON pin. This is determined by the value of the TON
resistor chosen (R1 in the Functional Block diagram) and the
magnitude of the input voltage, VIN. Under a specific set of
conditions, an on-time can be set that then dictates the switching
frequency. This switching frequency remains reasonably constant throughout load and line conditions as the on-time varies
inversely with the input voltage.
At the beginning of the switching cycle, the buck switch is turned
on for a fixed period that is determined by the current flowing
into TON. Once the current comparator trips, a one-shot monostable, the On Timer, is reset, turning off the switch. The current
through the inductor then decays. This current is sensed through
the external sense resistor (R2), and then compared against the
current-demand signal. After the current through the sense resistor decreases to the valley of the current-demand signal, the On
Timer is set to turn the buck switch back on again and the cycle is
repeated.
Disable/Enable The regulator is enabled by pulling the DIS pin
low. To disable the regulator, the DIS pin can simply be disconnected (open circuit).
Shutdown The regulator is disabled in the event of either an
overtemperature event, or an undervoltage on VIN (VINUV) or on
an internal housekeeping supply.
As soon as any of the above faults have been removed and
assuming DIS = 0, the output is restored.
Switch On Time and Switching Frequency The switch
on-time effectively determines the operating frequency of the
converter. To minimize the size of the power inductor and input
filtering it is recommended to run with as high a frequency
as possible. The MOSFET drivers are optimized to minimize
switching losses.
An important consideration in selecting the switching frequency
is to ensure that the on time (60 ns) and off time (350 ns) limitations are not reached under extreme conditions:
be achieved for a given number of LEDs and input voltage. Note
that it is highly recommended that worst case values are used
when considering any design.
Input Voltage
Switching
Frequency
(MHz)
12 V
24 V
LED
Quantity Span Quantity
of LEDs Voltage of LEDs
(V)
36 V
LED
Span
Voltage
(V)
Quantity
of LEDs
LED
Span
Voltage
(V)
2.0
1
3.5
2
7.0
3
10.5
1.7
1
3.5
3
10.5
4
14.0
1.0
2
7.0
4
14.0
6
21.0
0.300
3
10.5
6
21.0
9
31.5
The switch on time is programmed by the current flowing into
the TON pin. The current is determined by the input voltage, VIN ,
and the resistor, R1. The on time, Ton , can be found:
R1
Ton =
+ 10 × 10–9 .
VIN × 2.05 × 1010
(1)
To calculate the actual switching frequency, fsw , the Ton from the
above calculation can be used in conjunction with the transfer
function of the converter, as follows:
fSW =
1
VOUT + Vf
×
VIN + Vf
Ton
.
(2)
A simplified approach to selecting the Ton resistor (R1), to
accomplish an approximate switching frequency, can be found
from the following formula:
R1 =
VIN × 2.05 × 1010
fSW
.
(3)
Figure 1 illustrates a range of switching frequencies that can be
achieved with a given resistor and LED voltage. Each LED is
assumed to have a voltage drop of 3.5 V.
• the minimum off time occurs at minimum input voltage
High Brightness LED Driving
The A6210 can be configured as a very simple, low cost, high
brightness LED driver. The solution can drive high brightness
LEDs up to more than 3 A, while achieving very high efficiencies, in excess of 90%.
The following table takes into account the above maximum off
time figure and outlines the typical switching frequencies that can
The solution uses valley current mode control. This architecture
is optimized for high switching frequencies, allowing the use
• the minimum on time occurs at maximum input voltage
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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5
A6210
3 A, 2 MHz Buck-Regulating LED Driver
of physically small, low value inductors. An output capacitor is
not necessary either to reduce the ripple current or to close the
control loop.
High efficiencies are achieved via drive circuits optimized to
minimize switching losses and the current sense voltage has a
typical voltage drop of only 183 mV. The current in the LED
string can be pulse width modulated (PWM) via the DIS (Disable/Enable) pin. See figure 4.
Note: Vf is the forward voltage drop of the recirculation diode
and sense resistor (R2). The valley current is determined by the
sense voltage (183 mV) divided by the sense resistor.
Worked example
This example uses the brief specification outlined in the typical
application circuit on page 1. The following information is used
as a starting point:
The actual current control is maintained on the valley of the current ripple. The average LED current is the valley level plus half
the inductor ripple current, as shown in figure 2.
VIN = 24 V ,
To avoid potential mistriggering issues, it is recommended that
the ripple current that flows through the sense resistor (R2) does
not develop a ripple voltage of less than 20 mV.
ILED = 500 mA, and
The average LED current can be found from:
Iav
IRIPPLE
= IVALLEY + 2
(4)
,
LED ripple current, IRIPPLE = 60 mA .
The duty cycle can be found initially. Assume the forward voltage
drop of the re-circulation diode is 400 mV, and that the sense
resistor is 183 mV. Then:
substituting values:
Iav =
3 LEDs producing VLED = 12 V ,
183 mV  1 VIN –VLED
× ton
+  ×
L
R2
 2




(5)
,
VLED +Vf
12 + 0.58
0.39
D=
VIN +Vf = 24 + 0.58 =
where:
ton
VLED +Vf
1
= V +V ×
f
IN
f
SW
.
(7)
One of the objectives is to maximize the switching frequency to
(6)
.
minimize the inductor value. When driving at very high switching
frequencies, the duty cycle may be limited due to the minimum
2000
ton + toff = 1/ fSW
1800
1400
1 LED
2 LEDs
ton
toff
1/ I
2 RIPPLE
4 LEDs
Current
fSW (kHz)
1600
3 LEDs
5 LEDs
1200
1000
Valley Current
800
0
600
400
104
Average
LED Current
Time
105
106
Resistor, R1 (kΩ)
Figure 1. Switching frequency versus value of external resistor R1 on the
TON pin.
Figure 2. Current control
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115 Northeast Cutoff
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6
A6210
3 A, 2 MHz Buck-Regulating LED Driver
off-time of 350 ns. A minimum off-time is required to ensure the
bootstrap supply operates correctly. It can be shown that:
1–D
fSW =
toff (min)
(8)
,
where toff is 350 ns maximum.
a margin of at least 20% be allowed. In this example, the inductor
current rating, IL , should be:
IL ≥ 1.2 × (500 × 10–3 + 60 × 10–3 / 2) = 636 mA .
The valley control current is simply the average LED current
minus half the ripple current. Therefore:
Therefore:
fSW
1 – 0.51
= 350 × 10–9 = 1.4 MHz
IVALLEY = Iav –
.
= 500 × 10–3 –
The ton resistor (R1) value can be found:
VLED × 2.051 × 1010
fSW
12 × 2.051 × 1010
=
= 176 × 103 .
1.4 × 106
Choose R1 = 180 kΩ.
R1 =
(9)
(11)
60 × 10–3
= 470 mA
2
.
The sense resistor (R3) value can be found:
VSENSE
IVALLEY
183 × 10–3
=
= 0.36
470 × 10–3
(12)
R3 =
The inductor (L1) can now be found using the target LED ripple
current of 60 mA:
(V – VLED) × D
L1 = IN
IRIPPLE × fSW
(24 – 12) × 0.51
= 72 × 10–6 .
=
60 × 10–3 × 1.4 × 106
IRIPPLE
2
(10)
Choose L1 = 68 μH.
The inductor current rating should exceed the average current
plus half of the ripple current. In addition, it is recommended that
.
Choose R3 = 390 mΩ.
The ripple voltage developed across the sense resistor (R2) is
60 mA × 390 mΩ = 23 mV, which is greater than the minimum
required value of 20 mV.
Measured switching waveforms
From figure 3, it can be seen that the average current through
the LED string is 484 mA. This represents an error of 3.2% with
respect to the target current of 500 mA.
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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7
A6210
3 A, 2 MHz Buck-Regulating LED Driver
LED ripple current
ILED
484 mA
Ch1
VLX
Average LED Current
Ch2
t
Symbol
Ch1
Ch2
t
Parameter
VLX
ILED
time
Units/Division
5V
100 mA
200 ns
Figure 3. Switching voltage versus current through L1 and LED string
ILED
ILED
494 mA
494 mA
Average
LED Current
Average
LED Current
Ch1
Ch2
VLX
Ch1
Ch2
t
VLX
t
(A)
(B)
Symbol
Ch1
Ch2
t
Parameter
VLX
ILED
time
Units/Division
5V
100 mA
1 ms
Figure 4. PWM on DIS pin at 400 Hz: (A) narrow duty cycle, (B) wide duty cycle.
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115 Northeast Cutoff
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8
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Other Application Circuits
Application Circuit 1
VIN
42 V
C1
1.0 μF
R1
910 kΩ
BOOT
VIN
C2
22 nF
L1
47 μH
LX
R3
910 kΩ
A 6210
Name
D1
LED
Assembly
ISEN
TON
R2
150 mΩ
PWM or Switch
DIS
NC
Suggested Parts
SGND
GND
C1
C2
D1
L1
R1, R3
R2
Description
Manufacturer - Part Number
1 μF, 25V, X5R or X7R ceramic, 1210
22 nF, 50V, X5R or X7R ceramic, 0805
3 A, 60 V, Schottky diode
47 μH, 1.4 A inductor
910 kΩ, 1%, 0603
150 mΩ, 1%, 1206
Taiyo Yuden, TDK
Taiyo Yuden - NR 8040T 470M
Average LED current = 1.34 A
Peak to peak current = 200 mA
LED Assembly voltage = 24 V
Switching frequency = 1.0 MHz
Efficiency = 90.5%
Channel 1 – Current through inductor and LED Assembly, Channel 2 – Main switching voltage (LX node)
Plot 1. Average current = 1.34 A
Plot 2. Peak to peak current = 200 mA
Plot 3. PWM frequency = 10 kHz, maximum duty cycle
Plot 4. PWM frequency = 10 kHz, minimum duty cycle
Plot 5. Plot 4 with expanded time scale
Plot 6. PWM frequency = 10 kHz, turn off
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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9
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Application Circuit 2
VIN
24 V
BOOT
VIN
C1
1.0 μF
C2
22 nF
L1
22 μH
LX
R1
310 kΩ
A 6210
Name
D1
R2
150 mΩ
PWM or Switch
NC
LED
Assembly
ISEN
TON
DIS
Suggested Parts
R4
180 mΩ
SGND
GND
C1
C2
D1
L1
R1
R2
R4
Description
Manufacturer - Part Number
1 μF, 25V, X5R or X7R ceramic, 1210
22 nF, 50V, X5R or X7R ceramic, 0805
3 A, 60 V, Schottky diode
22 μH, 2.8 A inductor
310 kΩ, 1%, 0603
150 mΩ, 1%, 0805
180 mΩ, 1%, 0805
Taiyo Yuden, TDK
Coilcraft - MSS1048-223ML
Average LED current = 2.4 A
Peak to peak current = 260 mA
LED Assembly voltage = 15 V
Switching frequency = 1.0 MHz
Efficiency = 94%
Channel 1 – Current through inductor and LED Assembly, Channel 2 – Main switching voltage (LX node)
Plot 1. Average current = 2.4 A
Plot 2. Peak to peak current = 260 mA
Plot 3. PWM frequency = 10 kHz, maximum duty cycle
Plot 4. PWM frequency = 10 kHz, minimum duty cycle
Plot 5. Plot 4 with expanded time scale
Plot 6. PWM frequency = 10 kHz, turn off
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Package EU, 16-Contact QFN
0.35
4.00 ±0.15
1
0.65
16
16
0.95
A
1
2
2
4.00 ±0.15
2.70
4.10
2.70
4.10
17X
D
SEATING
PLANE
0.08 C
0.30 ±0.05
0.75 ±0.05
0.65
C
C
PCB Layout Reference View
For Reference Only
(reference JEDEC MO-220WGGC)
Dimensions in millimeters
Exact case and lead configuration at supplier discretion within limits shown
A Terminal #1 mark area
B Exposed thermal pad (reference only, terminal #1
identifier appearance at supplier discretion)
0.40 ±0.10
B
2.70
2
1
C Reference land pattern layout (reference IPC7351
QFN65P400X400X80-17W2M)
All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary
to meet application process requirements and PCB layout tolerances; when
mounting on a multilayer PCB, thermal vias at the exposed thermal pad land
can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5)
D Coplanarity includes exposed thermal pad and terminals
16
2.70
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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11
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Revision History
Revision
Revision Date
Rev. 2
May 2, 2011
Description of Revision
Minor edit
Copyright ©2008-2013, Allegro MicroSystems, LLC
Allegro MicroSystems, LLC reserves the right to make, from time to time, such departures from the detail specifications as may be required to
permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that
the information being relied upon is current.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its
use; nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12